Method and apparatus for transporting chain

ABSTRACT

The invention relates to methods and apparatus for storing at least one chainon an offshore service vessel. The chain is stored in a carousel on the vessel which is driven to rotate while the chain is being loaded into the carousel.

INTRODUCTION

The present invention relates to storage of chain such as mooring chainon an offshore service vessel used in the marine oil and gas industry.The invention also relates to transportation and installation of suchchains, and to a storage apparatus.

Heavy metal chain is a vital element of most mooring installationsoffshore. The storage, transportation and installation of mooring chainsoffshore is conventionally performed by loading chain into bins or“chain lockers”. Chain lockers are large, cuboid structures and thechain or chains are loaded into the chain lockers one at a time. Theorder of recovery from these chain lockers is usually “first chainin/last chain out”, so selecting one particular chain from the chainlocker can be difficult if the required chain is at the bottom of thepile.

To make recovery of a selected chain easier, a respective chain lockercan be provided for each individual chain. However, providing aplurality of (smaller) lockers instead of one large locker restricts thelength of chain that can be installed into each locker. Thus, any longchains might have to be split between two lockers, and this loading andunloading can be difficult to perform safely and efficiently.

According to a first aspect of the present invention there is provided amethod of storing at least one chain on an offshore service vessel, themethod comprising storing the chain on a rotatable carousel on thevessel, the carousel being driven to rotate while the chain is beingloaded into the carousel.

“Offshore service vessel” means any vessel specialised for theexploration, development, or production phases of oil and gas at sea.Pipelaying vessels for handling flexible pipeline and umbilicals arecommonly provided with carousels which can be adapted for chaintransportation in the manner of the invention. A carousel is a storagechamber, generally cylindrical, which is mounted on bearings or rollersso as to rotate around a vertical axis as a flexible pipeline or otherproduct is fed in or drawn out. Motors are provided to drive therotation.

An advantage of using a carousel also for chain storage is that thechain can be laid flat on the base of the carousel, reducing the risk oftwists or entanglement of the chain. This contrasts with loading a chaininto a chain locker, where the chain is piled up on itself in thelocker. Laying the chain(s) flat on the base of the carousel alsoreduces the centre of gravity of the chain(s), in comparison to chainspiled up in chain lockers. This improves the stability of the vessel. Afurther advantage is that carousels can allow easy access to variousdifferent stored chains; not only to the last chain loaded therein.Also, in many cases, either end of the required chain can be accessed,provided that such access is not prevented by other parts of the samechain, or another chain, being on top of the two ends.

A further advantage of using a carousel is that the chain can be loadedinto the carousel with accessories attached, for example, ballast clumpweights, end assemblies and/or special connections.

In contrast, considering again the prior art, storing chain withattached accessories in a chain locker is not possible for two reasons.Firstly, a “gypsy” wheel (a pocketed wheel) is conventionally used toload mooring chain into a chain locker. Gypsy wheels are generallywheel-shaped, and have “pockets” which receive the chain. They functionto pull the chain up from the deck and turn it through 90 degrees,letting it pile up in the chain locker under gravity. The chain fitsquite snugly within the pockets of the gypsy wheel, without a great dealof clearance. Therefore, any accessories (appurtenances) must bedetached from the chain before the chain is loaded into the gypsy wheel,in order for the chain to fit. Hence, the accessories must be storedseparately from the chain lockers, and must be attached to the chainoffshore. With some embodiments of the present invention, using a gypsywheel can be avoided by using a crane to control the loadinginto/unloading of the chain from the carousel. The chain can be handledin sections by the crane, so that the loading/unloading is accomplishedin a series of small steps.

Secondly, even without the problems caused by gypsy wheels, accessoriescannot be stored together with the chain in chain lockers. Chain lockersbeing merely large bins, a chain loaded into a chain locker piles up onitself in an irregular way, with many u-turns and acute angles. Hence,any accessories would risk becoming damaged in the loading process andthrough being stored like this, with a large amount of weight crushingthe lower, irregularly arranged parts of the chain.

In contrast, the carousel of the present invention can be used to layout the chain in a regular circular/spiral path, without u-turns, acuteangles or doubling-back, which provides much better protection for anyattached accessories. Furthermore, to increase the protection further,packing material may be laid down around the accessories. Hence, thecarousel allows provision for protection of sensitive components, suchas ballast clump weights or other accessories, during and followingloading.

Hence, the present invention has the advantage that accessories can bestored together with the chain, and do not have to be attached offshore.

Optionally, the carousel is located under the vessel's deck.

Optionally, the carousel may be a carousel of the vessel which isconventionally used to store flexible pipe and umbilicals. Hence, alarge amount of additional equipment is not necessarily required tocarry out the invention. Thus, such methods are efficient throughduplication of use of pre-existing equipment.

Such carousels have a large base area, so that a large number ofchains/length of chain, can be laid out directly on the base of thecarousel. This also reduces the centre of gravity of the chain(s), andimproves the stability of the vessel. This also avoids having to handlelong chain lengths into two chain lockers.

Alternatively, the carousel may be located above the vessel's deck.

Typically, the method includes storing a plurality of chains in thecarousel.

Hence, it is not necessary to provide a respective housing (e.g. chainlocker) for each chain.

Optionally, the method includes positioning one or more dividers withinthe carousel, to separate different chains from each other.

This helps prevent the different chains from becoming entangled witheach other, and also facilitates selection of a particular chain.

Additionally, the divider(s) may be used as an anchoring point toseafasten (fasten in a sufficiently seaworthy way) the chain fortransit.

Rotating the carousel facilitates the loading process, as the carouselcan be rotated as the chain is paid out, to lay down the chain in acircular or spiral path.

Typically, the method includes the step of laying down a plurality ofchains in the carousel at different radial distances from the centre ofthe carousel.

This allows easy selection of a selected chain for installation, incontrast to having a number of chains piled on top of each other in asingle chain locker. In some cases, the chains can be picked up byeither end. Furthermore, laying the chains out at different radialdistances (as opposed to on top of each other in chain lockers) reducesthe centre of gravity of the chains, increasing the stability of thevessel.

Typically, the chain is loaded into the carousel under tension. Forexample, a wire can be attached between a leading end of the chain and apadeye (fixing ring) attached to the carousel, to fix the leading end ofthe chain relative to the carousel.

Optionally, such tension can be created by causing the path of the chaininto the carousel to be inclined relative to the vertical, with thetouchdown point of the chain being at a different circumferentialposition from the circumferential position of the chain as it enters thecarousel.

For example, the circumferential position of the spooling device and/orthe rotational position of the carousel can then be controlled to ensurethat the touchdown point of the chain is circumferentially leading therest of the chain (leading being defined in the direction of rotation ofthe carousel).

This keeps the chain under tension and prevents slack from beingintroduced into the chain, which could otherwise occur if the chain wereallowed to drop directly downwards from the spool, without being undertension.

The weight of the chain typically also resists any dragging of the chainalong the base of the carousel by the spooling device, and thus alsohelps to keep the chain in tension.

Optionally, the chain has at least one attached accessory which remainsattached to the chain during the step of loading the chain into thecarousel. This accessory/accessories could be, for example, ballastclump weights, end assemblies and/or special connections.

The method may include the step of adding protective packing materialaround the chain and attached accessory in the carousel. This providesadditional protection for any fragile elements of theaccessory/accessories.

Typically, the method includes the step of rotating the carousel ineither rotational direction, as required.

Optionally, the method includes also storing at least one other type ofproduct in the carousel in addition to the chain. The other type ofproduct may optionally be flexible product, umbilicals and/or fibre orsteel wire, but is not limited to these.

Typically, the method includes the step of transporting the chain in thecarousel.

Optionally, the method includes the step of installing the chainoffshore. In the following description, removing the chain from thecarousel is described as part of the installation procedure.

Typically, the step of installing the chain includes rotating thecarousel in a direction of rotation that is dependent on which end ofthe chain is to be installed first. For instance, if the trailing end ofthe chain in the loading process is to become the leading end forinstallation, the direction of rotation of the carousel for loading thechain into the carousel would typically be the opposite direction tothat used for removing the chain from the carousel for installation.Hence, the path that the chain takes into and out from the carousel isreversed, by reversing the carousel direction. In contrast, if theleading end of the chain in the loading process is also to be theleading end for installation, the direction of rotation of the carouselfor loading and installing the chain would typically be the same.

Optionally, the step of loading the chain into the carousel and/or thestep of installing the chain (bringing it out of the carousel) mayinclude using a crane to lower/raise the chain in sections. Hence, agypsy wheel is not essential for loading/unloading the chain, althoughfor lengths of simple chain a gypsy wheel presents an efficient solutionfor controlling the chain.

According to a second aspect of the invention there is provided the useof a rotatably driven carousel on board an offshore service vessel tostore chain on the vessel.

According to a third aspect of the present invention there is providedapparatus for storing at least one chain on an offshore service vessel,comprising a carousel which is rotatably mounted on the vessel, a chainloading system adapted for loading the chain into the carousel and drivemeans for rotating the carousel as the chain is loaded into thecarousel.

Optionally, the chain loading system comprises chain guide means, forcontrolling the radial distance of the chain touchdown point from thecentre of the carousel.

Typically, the chain guide means comprises a spooling device.

Typically, the chain guide means comprises a chute, the position ofwhich can be adjusted to control the touchdown point of the mooringchain.

Optionally, the orientation of the chute is adjustable. For example, theangle of the chute can be varied to direct the mooring chain to aradially inner, outer, or middle part of the carousel. This can be doneby having a fixed upper end of the chute, and a lower end which ismoveable in the radial direction with respect to the carousel.

Additionally or alternatively, the radial position of the chute withrespect to the carousel is adjustable. Hence, the entire chute can movein the radial direction, instead of just a lower end thereof.

The apparatus may comprise a lay system for laying flexible pipe,provided with adaptations for chain handling. One such adaptation may beone or more pocketed wheels or “gypsy wheels”. Such wheels may be drivenand/or passive in operation.

Alternatively, the chain guide means can include a moveable spoolingarm, which can be moved to control the touchdown point of the chain.

In such cases, the chain guide means may also include a chute which hasa width that increases towards a chute mouth, to permit the mooringchain to leave the chute in a selected one of a plurality of differentdirections, according to the position of the moveable spooling arm.

Alternatively, the chain guide means comprises a crane. A crane can beadvantageous if an accessory/accessories is attached to the chain.

Optionally, the chain loading system includes a gypsy wheel.

Optionally, the apparatus includes attachment means, by which a chaincan be attached to the carousel. Optionally, the attachment meanscomprises at least one padeye, which may be located on a base of thecarousel.

Typically, the carousel is adapted to rotate in both rotationaldirections (clockwise and anti-clockwise), as required.

These and further features and advantages of the invention will beunderstood by the skilled reader from a consideration of the embodimentdescribed below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, and with reference to the following drawings, in which:

FIG. 1 shows a partially cut-away side view of an offshore servicevessel with a mooring chain being loaded into a carousel, illustratingthe principles of the invention;

FIG. 2 shows a plan view of the vessel of FIG. 1;

FIGS. 3 and 4 show plan views of the vessel of FIG. 1, showing twodifferent methods of loading a mooring chain into the carousel of thevessel from the shore;

FIG. 5 shows an enlarged view of a compartment of the FIG. 1 vessel,showing the carousel and mooring chain in more detail;

FIG. 6 shows a plan view of the carousel of FIG. 5, and also shows twoexemplary mooring chains located on the base of the carousel;

FIG. 7 shows a partially cut-away side view of the carousel of thevessel of FIG. 1, with a mooring chain being loaded into the carousel bya chain guide means according to a first embodiment of the invention;

FIG. 8 shows a plan view of the carousel of FIG. 7;

FIG. 9 shows a partially cut-away side view of the carousel of theoffshore service vessel of FIG. 1, with a mooring chain being loadedinto the carousel by a chain guide means according to a secondembodiment of the invention;

FIG. 10 shows a plan view of the carousel of FIG. 9;

FIG. 11 shows a partially cut-away side view of the carousel of thevessel of FIG. 1, with a mooring chain being loaded into the carousel bya chain guide means according to a third embodiment of the invention;

FIG. 12 shows a plan view of the carousel of FIG. 11;

FIG. 13 shows a partially cut-away side view of the carousel of thevessel of FIG. 1, with a mooring chain and attached accessories beingloaded into the carousel by a chain guide means according to a fourthembodiment of the invention; and

FIG. 14 shows a plan view of the carousel of FIG. 13.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

Referring to FIGS. 1 and 2, an offshore service vessel comprises a hull100 with a superstructure 102, located forward of a larger working area.The vessel has various thrusters 104 to provide dynamic positioning(position holding) during operations of the vessel, for example pipelaying and mooring chain installation.

The vessel also has a deck 109. For the storage, transportation andinstallation of mooring chain, a carousel 110 is provided, located belowthe level of the deck 109, in a compartment 112. The compartment 112 hasa floor 114 and its ceiling is the deck 109. A loading hatch 116 in thedeck 109 provides access to the compartment 112. The loading hatch 116is rectangular and has a length 117 (longer dimension) and a width 118(shorter). The vessel also has a crane 120, which has a crane arm A anda hook H.

The carousel 110 will be described in use for the storage andtransportation of chains, but can optionally also be used for thestorage and dispensing of flexible product, as will be explained below.Indeed, in this embodiment, the vessel is substantially a pre-existingvessel and the carousel 110 is a carousel which is conventionally usedfor storage of flexible product such as pipe and umbilicals. However, inother embodiments, the carousel 110 could be used for the storage anddispensing of flexible product, and a further, additional carousel couldbe provided, above or below the deck 109, for mooring chain. Hence, thelocation of the carousel for the mooring chain is not an essentialelement of the invention.

Further carousels and storage space (not shown) may also be provided,which can additionally or alternatively be used for flexible product, orother equipment.

FIG. 1 shows (schematically) a mooring chain 332 being loaded onto thecarousel 110 from the deck 109, through the loading hatch 116.

FIGS. 3 and 4 show two variations of how the mooring chain can be loadedinto the carousel 110 from the shore. In FIG. 3, the vessel is moored byropes/chains 118 to a dock 120. The mooring chain 332 is stored on thedock, is brought onto the deck 109, and is then guided through a turn of90 degrees so that it enters the loading hatch 116 from a directionparallel to the width 118 of the loading hatch 116. In FIG. 4, theprocedure is similar except that the mooring chain 332 enters theloading hatch 116 from a direction parallel to its length 117.

Referring now to FIGS. 5 and 6, the schematic view of the mooring chain332 and the carousel 110 is shown in more detail. The carousel 110comprises a base 312, an outer cylindrical wall 314, and an innercylindrical wall, which forms a hub 316 of the carousel 110. The outercylindrical wall 314 is provided at the radially outermost extent of thebase 312. The base 312, the outer cylindrical wall 314 and the hub 316together define a body 317 of the carousel 110, in which mooring chaincan be stored.

The base 312 is located on a support plate 319, which includes anupwardly-extending hub support 318 at its centre, which also correspondswith the centre of the base 312.

The hub support 318 has an upper bearing surface, on which the base 312is directly mounted. Also between the base 312 and the support plate 319various bearings 320 (e.g. slide bearings or roller bearings) which arelocated radially outwards of the hub support 318. Hence, the body 317 ofthe carousel 110 is rotatably mounted on the support plate 319. Thesupport plate 319 is, in turn, located on the floor 114 of thecompartment 112.

As shown in FIG. 6 (but not FIG. 5), a divider 322 can be providedwithin the body 317 of the carousel 110. The divider 322 divides aradially inner volume of the body 317 from a radially outer volume. Thedivider 322 comprises posts or bollards 324, arranged in a circular pathon the base 312 and which are linked together by ropes 326 to form afence-like structure.

The position of the divider 322 is not necessarily fixed where it isshown in FIG. 6, and could be located closer to, or further away from,the hub 316, or moveable to adjust the relative sizes of the inner andouter storage volumes. Furthermore, in some embodiments, a plurality ofdividers 322 could be used, at different radii from the hub 316. Forexample, two dividers could be used to provide three separate volumeswithin the body 317 of the carousel 110, and similarly if even moreseparate volumes are required.

Typically, the divider(s) 322 may be used to separate different mooringchains from each other. However, it is also possible to store otherflexible product one side of a divider and mooring chain(s) on the otherside of the divider. Hence, in this way, the carousel 110 could be usedfor the storage and dispensing of both mooring chain and flexibleproduct.

Also shown in both FIGS. 5 and 6 are various mooring chains. In FIG. 6,a first mooring chain 328 is shown laid out on the base 312 at aradially inner position, next to the hub 316. The mooring chain 328 islaid out in a spiral configuration, starting in contact with the hub316, and gradually increasing in radius, such that after onecircumference (circuit) of the hub 316 has been completed, a secondcircuit starts, not on top of the first circuit, but also on the base312 at a slightly increased radius.

The first mooring chain 328 has a lead wire 334 attached to a leadingend 328 a of the chain 328. The lead wire 334 is fixed to a padeye (notshown) on the body 317 of the carousel, typically on the base 312. Thisfixes the leading end 328 a in position. The first mooring chain 328also has a trailing wire 336 attached to a trailing end 328 b of thechain 328.

Also shown in FIG. 6 is a second mooring chain 330, which is located ata radially outer position, next to the outer cylindrical wall 314. Thesecond mooring chain 330 extends along a portion of the outercylindrical wall 314. Hence, the mooring chains 328, 330 are laid downin the carousel 110 at different radial distances from the centre of thecarousel 110. Both of the mooring chains 328, 330 are laid flat on thebase 312 of the carousel 110, which keeps the centre of gravity of bothchains 328, 330 as low as possible.

The second mooring chain 330 has a lead wire 338 attached to a leadingend 330 a of the chain 330. The lead wire 338 is fixed to a padeye (notshown) on the body 317 of the carousel, typically on the base 312. Thisfixes the leading end 330 a in position. The second mooring chain 330also has a trailing wire 340 attached to a trailing end 330 b of thechain 330.

Typically both chains 328, 330 will be longer than shown, and will varyin size; FIG. 6 is merely illustrative of the concept. If the firstmooring chain 328 was longer, it might cover the entire area of the base312 between the hub 316 and the divider 322. Furthermore, once this areahas been covered, the chain 328 could be laid out, still in a spiralform, on top of the already-laid down chain 328, in a second verticallayer, and so on, if third, fourth, etc. layers are required. The sameapplies to the second mooring chain 330.

Optionally, more than two chains can be stored in the carousel 110,either with or without additional dividers 322. Optionally, enoughdividers 322 would be provided to separate each chain from the others.

FIG. 5 shows the exemplary mooring chain 332 (which could be the firstmooring chain 328, the second mooring chain 330, or a further mooringchain) being loaded into the carousel 110, using a chain loading system342 (shown schematically). The chain loading system 342 is adapted forloading mooring chain into the carousel.

The chain loading system 342 comprises chain guide means 344, forcontrolling the radial distance of the chain touchdown point from thecentre of the carousel 110. The chain guide means 344 comprises aspooling device, which is moveable to different radii relative to therotational axis of the carousel 110, to lay down the chain 332 at aselected radius. In FIG. 5, the chain guide means 344 is moveable in adirection that is parallel to the length 117 of the loading hatch 116(the direction perpendicular to the plane of view of FIG. 5). The chain332 in FIG. 5 is in front of the hub 316 (“in front” defined byreference to the viewing axis) and is not inside the centre of the hub316.

A schematic example of the novel method of storing mooring chain willnow be explained with reference to FIGS. 5 and 6. The method in thisexample comprises storing a pair of mooring chains on a carousel 110 onthe vessel.

The method may include positioning dividers within the carousel 110, toseparate different mooring chains from each other. In FIGS. 5 and 6, asingle divider 322 is used, to separate two mooring chains from eachother. The divider 322 (or plurality of dividers if required) istypically installed in the body 317 of the carousel 110 before loadingany mooring chains into the carousel 110, although this is notessential.

Typically, part of the chain loading system is used to raise the mooringchain from the deck up to the chain guide means 344, with which it isengaged. Referring to FIG. 5, the mooring chain 332 (which at this stagein the method is the first mooring chain 328) is fed into the body 317of the carousel 110 by the chain loading system 342. The chain guidemeans 344 is set to a selected radial distance from the hub 316 (e.g.adjacent to the hub 316 in this example). The chain loading system 342then lowers the leading end 328 a of the chain 328 onto the base 312.

The lead wire 334 attached to the leading end 328 a of the chain 328 cannow (or earlier in the method) be fixed to a padeye (not shown) on thebody 317 of the carousel, typically on the base 312. This fixes theleading end 328 a in position.

As the chain 328 lands on the base 312, the body 317 of the carousel 110is progressively rotated relative to the support plate 319, to presentan uncovered part of the base 312 to the following links of the chain328 as they land on the base 312. Also, at the same time, the chainguide means 344 is moved very gradually in the radially outwarddirection (towards the viewer of FIG. 5). The combined result of therotation of the base 312 and the movement of the chain guide means 344is that the chain 328 is laid down in a spiral path around the hub 316as shown in FIG. 6.

Typically, the circumferential position of the chain guide means 344and/or the rotational position of the carousel 110 is controlled toensure that the touchdown point of the chain 328 is circumferentiallyleading the rest of the chain (leading being defined in the direction ofrotation of the carousel 110). The touchdown point of the chain 328 istypically one or two metres in advance of the chain 328 at the chainguide means 344. This is possible because the leading end 328 a of thechain 328 has already been fixed to the carousel 110.

Hence, tension is created in the chain 328 by causing the path of thechain into the carousel to be inclined relative to the vertical, withthe touchdown point of the chain being at a different circumferentialposition from the circumferential position of the chain 328 as it entersthe carousel 110. This helps ensure that the chain 328 is kept undertension as it is paid out, which prevents slack from being introducedinto the chain 328. Hence, the mooring chain 332 is loaded into thecarousel 110 under tension.

The weight of the mooring chain 328 also resists any dragging of thechain 328 along the base 312 by the chain guide means 344, and thus alsohelps to keep the chain 332 in tension.

The rotation of the base 312 and the radial movement of the chain guidemeans 344 is continued until the chain 328 has been fully laid out. Ifthe chain 328 covers the entire area of the base 312 between the hub 316and the divider 322 before being fully laid out, a second layer of thechain 328 can be loaded on top of the first layer, also in a spiralconfiguration, and so on. Hence, the chain 328 can be of any length.

After sufficient turns of the carousel, the trailing end of the chainwill be reached. The trailing wire 336 is used to support the trailingend 328 b as it is lowered into the carousel 110.

After the first chain 328 has been fully laid out, the radial positionof the chain guide means 344 is adjusted (moved radially outward, inthis example). The chain loading system 342 is then used to lay down thesecond mooring chain 330 into the body 317 of the carousel 110, on theradially outer side of the divider 322. This is done using a method verysimilar to that described above for the chain 328. Hence, the twomooring chains are laid down in the carousel at different radialdistances from the centre of the carousel 110, on either side of thedivider 322.

Optionally, the method can include fastening (seafastening) one or bothmooring chains to the divider 322, by any suitable means. Optionally,packing can be put down around the chains (and any attached accessories)to provide additional protection.

Various alternative methods and apparatus for loading a chain into thecarousel will now be explained with reference to FIGS. 7 and 8; FIGS. 9and 10; FIGS. 11 and 12; and FIGS. 13 and 14, which are all variationson the generic method of FIGS. 5 and 6. All that varies in thesealternative examples is the chain loading system.

In the example of FIGS. 7 and 8, a chain loading system 342 a includes apocketed wheel known in the art as a gypsy wheel 346 a, mounted on thedeck 109. The chain loading system 342 a also includes a chain guidemeans 344 a, which includes a chute 348 a (best shown in FIG. 8) and amoveable spooling arm 350. The chute 348 a is shaped like half a pipe,and is mounted on the deck 109, with a mouth M of the chute 348 a beingabove the loading hatch 116. The chute 348 a increases in width in thedirection towards its mouth M, and also curves downwards slightly at themouth M, leading the chain 332 into the compartment 112. The moveablespooling arm 350 is mounted on the vessel at a fixed end, articulatedand activated by hydraulic rams. The arm 350 carries a wheel arrangement351 at its free end. The wheel arrangement 351 is adapted to engage thechain 332, by insertion partway into one of the chain links. Themoveable spooling arm 350 is adapted to move the wheel arrangement 351in the plane parallel to the base 312.

In use, the chain 332 is paid out by the gypsy wheel 346 a at acontrolled rate, passes over the chute 348 a, through the loading hatch116 into the compartment 112, where it lands on the base 312 of thecarousel 110. The spooling arm 350 can be moved as required to controlthe touchdown point of the mooring chain 332.

FIG. 8 shows two different possible (alternative) positions of the chain332. A first chain path P1 follows the contour of the hub 316, and iscaused by having moved the spool arm 350 to a radially inward position.The chain 332 is diverted by the spool arm 350 along the radially inneredge of the chute 348 a, and from there, continues radially inwards to atouchdown position close to the hub 316.

A second, alternative chain path P2 follows the contour of the outercylindrical wall 314, and is caused by having moved the spool arm 350 toa radially outer position. The chain 332 is diverted by the spool arm350 along the radially outer edge of the chute 348 a, and from there,continues radially outwardly to a touchdown position close to the outercylindrical wall 314.

Hence, moving the spooling arm 350 controls the path of the chain 332.The spooling arm 350 would typically be moved when beginning a new chain332, to lay the new chain down at a different radius. The spooling arm350 can also be moved whilst a chain is being laid out, to cause thechain to fall into a spiral rather than a circular path.

Referring to FIGS. 9 and 10, an alternative chain loading system 342 bincludes a gypsy wheel 346 b which is mounted on the deck 109 directlyabove the loading hatch 116. The chain loading system 342 b alsoincludes an alternative chain guide means, in the form of an elongatechute 348 b. The chute 348 b may be tubular, or in the form of ahalf-pipe.

An upper end of the chute 348 b is swivel-mounted on the vessel, so thatthe orientation of the chute 348 b is adjustable in a plane parallel tothe base 312. The chute 348 b is not shown in elevation, but has anincline to allow the chain 332 to slide down under gravity. The chute348 b can point around a large arc. Three possible orientations of thechute 348 b are shown in FIG. 10. An inward pointing orientation can beused to direct the chain 332 along an inner, radial path, adjacent tothe hub 316, and an outwardly pointing orientation can be used to directthe chain 332 to lie adjacent to the outer cylindrical wall 314, and aspectrum of intermediate positions can be used for all radii in between.As with the previous examples, the orientation of the chute 348 b can beadjusted as the chain 332 is laid out, to cause the chain 332 to fallinto a spiral path. The rest of the method has been described above withreference to FIGS. 5 and 6.

Referring to FIGS. 11 and 12, an alternative chain loading system 342 cincludes a gypsy wheel 346 c which is mounted on the deck 109. The chainloading system 342 c also includes an alternative chain guide means 344c, in the form of a chute 348 c on a linear spooling drive (not shown).The gypsy wheel 346 c is aligned so that the chain 332 coming from thegypsy wheel 346 c is parallel to the length 117 of the loading hatch116.

The spooling drive and chute 348 c sits partially in the loading hatch116 or just above it, and the chute 348 c is moveable in a directionparallel to the length 117 of the loading hatch 116. The linear spoolingdrive may for example comprise a carriage driven along support railsextending along the length of hatch 116, the carriage in turn supportingchute 348 c at a desired position.

As the length 117 of the loading hatch 116 runs substantially in theradial direction of the carousel 110, this means the chute 348 c isadjustable in radial position with respect to the carousel. The range ofmovement of the chute 348 c is indicated by the arrow X in FIGS. 11 and12. As shown in FIG. 11, the selected position of the chute 348 ccorresponds to a selected radius for the chain touchdown point on thebase 312. The range of touchdown radii is shown by arrow Y in FIG. 11.Thus, the radial position of the chute 348 c is adjustable to adjust thepath of the mooring chain 332 being laid down, e.g. in a spiral path, orfor a second chain to be laid down at a different radial position from afirst chain.

In each of these examples the chain is maintained in tension to controlits touchdown and coiling.

FIGS. 13 and 14 show a method and apparatus for handling a mooring chain332 a with attached accessories 360. The accessories 360 may be ballastclump weights, end assemblies and/or special connections, or other typesof accessories, for example.

Since a chain with accessories 360 cannot be handled by a gypsy wheel(because the accessories 360 are too bulky to fit in the wheel), thecrane hook H of the crane 120 is used to lower the chain 332 a into thecarousel 110 in stages. FIG. 14 shows the first chain 328, theinstallation of which has already been explained with reference to FIG.5, and the chain 332 a. The chain 332 a has been laid out on the base312 adjacent to the outer perimeter of the divider 322, “hugging” theouter perimeter. In this embodiment, the chain guide means is thereforeprovided by the crane 120 and the hook H, the hook H being moveable toadjust the touchdown position of the chain 332 a.

To increase the protection of the accessories 360, packing material (notshown) may be laid down around the accessories 360. Hence, sensitivecomponents can be protected during and following loading.

Thus, this example allows attached accessories 360 to loaded into thecarousel 110 together with the mooring chain 332 a. This is advantageousbecause the accessories 360 do not have to be stored separately from thechain 332 a on the vessel, and do not need to be attached to the chain332 a offshore.

Any of the above methods can also include the step of transporting themooring chain(s), by moving the vessel, with the mooring chain locatedin the carousel. The chain may be transported to an installation sitefor deployment into the sea, or may be recovered from the sea andtransported to another location.

Any of the above methods can also include the step of installing amooring chain. Since the chains 328, 330 are laid down at differentradial distances, a particular chain 328, 330 can be easily selected andpulled out of the carousel 110 for installation. The same equipment usedto load the chains 328, 330 will be used in unloading and installing thechains 328, 330.

The chains 328, 330 shown in FIG. 6 can be picked up by either end, asboth ends are accessible and are not covered up by further chains/partsof the same chain. Typically, the installation procedure is very similarto the chain-loading procedure, but in reverse. Thus, the chain loadingsystem 342 is also used in the process of picking up and installing themooring chains. A crane 120, gypsy wheel 346, or other equipment can beused to hoist the chain up from the body 317 of the carousel 110, asrequired.

As with the loading process, the carousel 110 is rotated to facilitatethe removal of the chain from the carousel 110. If the trailing end ofthe chain in the loading process is to become the leading end forinstallation, the direction of rotation of the carousel 110 for loadingin the chain would typically be the opposite direction to that used forinstallation. Hence, the path that the chain takes into and out from thecarousel is reversed, by reversing the carousel direction. Both endsneed not be accessible, so that the chain can be layered in the carouselif its length requires. Membranes may be deployed to separate the layersif appropriate.

In contrast, if the leading end of the chain in the loading process isto also be the leading end for installation, the direction of rotationof the carousel for loading and installing the chain would typically bethe same.

Once the chain has been selected and pulled out of the carousel 110, therest of the installation procedure is carried out, as is conventional.The mooring chain may, for example, be installed between a floating rigand the seabed, to anchor the floating rig in position. However, theinvention is not limited to any particular end use of the mooring chain.

Modifications and improvements can be incorporated without departingfrom the scope of the invention. For example, the size, dimensions andlocation of the carousel for mooring chain are not essential to theinvention and can be varied. As already stated above, it is notessential to use a carousel of the type usually used for storage anddispensing of flexible product. Optionally, a plurality of smallcarousels could be used, instead of one large carousel.

The offshore service vessel can be of any shape and design, and is notlimited to the exemplary vessel of FIG. 1. Apart from that the offshoreservice vessel must have a carousel, none of the other equipmentdescribed in relation to FIG. 1 is essential to the invention. Equally,the offshore service vessel may also include additional equipment andmay be designed for additional tasks not described above. The phrase“offshore service vessel” is not used in any limiting sense, so thatconstruction vessels are included, for example.

In some methods, the chain guide means 344 is not adjusted whilst thechain is being laid out, so that the chain is laid down in a circularpath, instead of a spiral path. For chain lengths shorter than onecircuit of the base 312 at that particular radius, this will make nodifference. For longer chain lengths, a second circular layer laid ontop of a first circular layer may in any case fall off the first layerand onto the carousel base 312. More orderly spooling is thus preferred.

1. A method of storing at least one chain on an offshore service vessel,the method comprising storing the chain in a rotatable carousel on thevessel, the carousel being driven to rotate while the chain is beingloaded into the carousel.
 2. A method as claimed in claim 1, wherein thecarousel is located under the vessel's deck.
 3. A method as claimed inclaim 1, including storing a plurality of chains in the carousel.
 4. Amethod as claimed in claim 3, including positioning at least one dividerwithin the carousel to separate different chains from each other.
 5. Amethod as claimed in claim 4, including using the divider as ananchoring point to seafasten the chain for transit.
 6. A method asclaimed in claim 1, including storing a plurality of chains in thecarousel, and wherein the method includes laying down the chains in thecarousel at different radial distances from the centre of the carousel.7. A method as claimed in claim 1, wherein the chain is loaded into thecarousel under tension.
 8. A method as claimed in claim 7, whereintension is created by causing the path of the chain into the carousel tobe inclined relative to the vertical, with the touchdown point of thechain being at a different circumferential position from thecircumferential position of the chain as it enters the carousel.
 9. Amethod as claimed in claim 1, wherein the chain is a mooring chain andhas at least one attached accessory which remains attached to the chainduring loading the chain into the carousel.
 10. A method as claimed inclaim 9, including adding protective packing material around the chainand attached accessory in the carousel.
 11. A method as claimed in claim1, including rotating the carousel in both rotational directions.
 12. Amethod as claimed in claim 1, including also storing at least one othertype of product in the carousel in addition to the chain.
 13. A methodas claimed in claim 1, including transporting the chain in the carousel.14. A method as claimed in claim 1, including installing the chainoffshore.
 15. A method as claimed in claim 1, wherein installing thechain includes rotating the carousel in a direction of rotation that isdependent on which end of the chain to be installed first. 16.(canceled)
 17. Apparatus for storing at least one chain on an offshoreservice vessel, comprising a carousel which is rotatably mounted on thevessel, a chain loading system adapted for loading the chain into thecarousel and drive means adapted for rotating the carousel as the chainis loaded into the carousel.
 18. Apparatus as claimed in claim 17,wherein the chain loading system comprises chain guide, for controllingthe radial distance of a chain touchdown point from the centre of thecarousel.
 19. Apparatus as claimed in claim 18, wherein the chain guidecomprises a spooling device.
 20. Apparatus as claimed in claim 18wherein the chain guide comprises a chute, the position of which can beadjusted to control the touchdown point of the chain.
 21. Apparatus asclaimed in claim 20, wherein the orientation of the chute is adjustable.22. Apparatus as claimed in claim 20 wherein the radial position of thechute with respect to the carousel is adjustable.
 23. Apparatus asclaimed in claim 18 wherein the chain guide includes a moveable spoolingarm which can be moved to control the touchdown point of the chain. 24.Apparatus as claimed in claim 23, wherein the chain guide also includesa chute which has a width that increases towards a chute mouth to permitthe chain to leave the chute in a selected one of a plurality ofdifferent directions according to the position of the moveable spoolingarm.
 25. Apparatus as claimed in claims 17 wherein the chain loadingsystem also includes a gypsy wheel.
 26. Apparatus as claimed in claim18, wherein the chain guide comprises a crane.
 27. Apparatus as claimedin claims 17 including an attachment by which a chain can be attached tothe carousel.
 28. Apparatus as claimed in claims 17 wherein the carouselis adapted to rotate in both rotational directions.